As a very relevant non-limiting example to which the present invention can be beneficially applied, it is disclosed that fabrication of MOSFET Transistors requires formation of a Gate Structure on a Semiconductor Substrate. Typical practice is to use Silicon as the Semiconductor Substrate, grow thermal SiO2 on its surface, (which is a dielectric material), and then apply metal atop thereof to form said Gate Structure. When Gate SiO2 thickness is below about 100 Angstroms, however, it becomes leaky and is subject to breakdown at too low of voltages applied to the metal. Investigation of deposited materials, other than SiO2 onto the Semiconductor for use as the dielectric material in Gate Structures, is therefore being pursued. However, control of the properties of the dielectric material formed during a fabrication procedure is sensitive to changes in the procedure, which changes are often difficult to detect and control. The present invention recognizes this fact and the fact that the first step in developing repeatability in fabrication is developing the ability to accurately monitor Gate dielectric materials. Methodology which enables accurate monitoring of materials allows identification of deviations from optimum which can be correlated to what are often subtle changes in fabrication procedure parameters, which subtle fabrication procedure changes are not readily obvious unless it is known to specifically look for their presence as a result of detected deviations from intended fabrication end-results.
Further, as alluded to above, application of a thin metal film atop Gate Oxide or other dielectric material is necessary during MOSFET fabrication. In that light it is disclosed that even ellipsometic investigation of ultra thin films of any composition when deposited atop a thin dielectric film, (eg. 30–100 Angstroms), often does not result in data which can be used to accurately determine the thickness of said film.
The methodology of the invention disclosed herein can be applied to investigate and/or control formation of thin films based upon differences in obtained and reference spectral data, or in data obtained at various times during fabrication.
An article titled “Data Analysis for Spectroscopic Ellipsometry”, Thin SOlid Films, 234 (1993) is disclosed as it defines parameters N=Cos(2Ψ); C=Sin(2Ψ)Cos(Δ) and S=Sin(2Ψ)Sin(Δ) which are applied in the preferred embodiment of the disclosed invention.
A search of patents which focus the use of electromagnetic radiation to monitor thin films or the fabrication of thin films, has provided the following:                U.S. Pat. No. 6,573,999 to Yang;        U.S. Pat. No. 6,349,594 to Yabe;        U.S. Pat. No. 5,486,701 to Norton et al.;        U.S. Pat. No. 5,798,837 to Aspnes et al.;        U.S. Pat. No. 4,105,338 to Kuroha;        U.S. Pat. No. 5,181,080 to Fanton et al.;        U.S. Pat. No. 4,826,321 to Coates et al.;        U.S. Pat. No. 5,910,842 to Piwonka-Corle et al.;        U.S. Pat. No. 5,517,312 to Finarov;        U.S. Pat. No. 6,278,519 to Rosenscwaig et al.;        U.S. Pat. No. 4,899,055 to Adams;        U.S. Pat. No. 5,798,837 to Aspnes et al.;        U.S. Pat. No. 5,793,480 to Lacey et al.;        U.S. Pat. No. 5,900,939 to Aspnes et al.;        U.S. Pat. No. 5,595,916 to Fujimura et al.;        U.S. Pat. No. 6,605,482 to Celii et al.; and        Patent Application No. US 2002/0176081 A1.Patents which discuss monitoring witness samples are:        U.S. Pat. No. 6,278,809 to Johnson et al.;        U.S. Pat. No. 5,871,805 to Lemelson.        
Even in view of the identified prior art, need remains for methodology which enables evaluating and optionally controlling formation of thin films.